Pipe condition detecting apparatus

ABSTRACT

The invention relates to apparatus and a method for detecting the condition of the material of a pipeline wall. The apparatus includes means for inducing and detecting magnetic flux at a location on the pipeline and, at said location, sensing means detect whether any change in material condition is on or near the external wall of the pipeline. By analysing the two sets of monitored values a change in condition, such as corrosion, can be detected, located and determined to be at or near the external or internal surfaces of the pipeline wall.

[0001] The invention to which this application relates is the provisionof apparatus and a method for detecting the condition of a pipe.

[0002] It is known to provide apparatus which can be used to assess thequality, damage, and/or risk of failure of pipelines which have been inservice for a period of time and, from the information provided by theapparatus and method, to then assess whether the pipe is in a dangerouscondition, needs specific maintenance and so on. This therefore avoidsthe need for the pipeline to be completely replaced and/or ensures thatif the pipeline is in a dangerous state of decay, it can be relativelyeasily identified without the need to excavate the entire pipe andreplace same.

[0003] A common, known, process, is to send an item of apparatus,typically known in the trade as a “PIG”, along the interior of thepipeline with the same being carried by the flow of the gas or liquid asit flows along the pipeline interior. As it passes along the interior ofthe pipe, results from a series of sensors and/or other detectionapparatus mounted on the PIG forms a survey of the pipeline interior andexterior condition. However, a problem is that this type of apparatus isnot always suitable or compatible with particular liquids or gases whichpass along the pipeline interior. For example, there is a generalresistance to allow “pigs” and other forms of apparatus to pass alongthe interior of a pipeline which carries water for fear of causingcontamination to the water. Thus, the use of pigs is generally regardedas being impractical or potentially dangerous to the quality of someliquids passing along the pipeline.

[0004] It is also known to provide apparatus which can travel along theexterior surface of a pipeline. This form of apparatus can be providedwith means to allow the same to be moved along the exterior of thepipeline. In one embodiment a magnetic flux is generated which passesinto the pipeline. As the apparatus moves along the pipeline, the levelof the magnetic flux level is monitored to ensure that any changes influx ate detected. This change can be caused by “leakage” and isindicative of reduced pipe wall thicknesses. As a result the possiblecorrosion or damage to the pipe wall is indicated and mapped withrespect to the position of the apparatus on the pipeline.

[0005] With many types of pipeline, this form of apparatus can besatisfactory in that the magnetic flux indicates the position of adefect and a subsequent inspection of the external surface of thepipeline indicates to the user whether the defect is on the externalsurface of the pipeline. If it is visible then magnetic flux can be usedto determine the depth of the fault but if not visible, the fault isthen assumed to be on the interior wall of the pipeline and the magneticflux change can again be used to determine the size and depth of thefault. This apparatus is therefore available for use where a visualcheck of the external pipeline can be used to determine the position ofthe defect indicated by a magnetic flux change.

[0006] However, with certain materials, such as for example cast iron,there may be defects on the exterior of the pipe which are not visibleand therefore the apparatus which is available at the present cannot beused as a visual check of the external surface is not guaranteed toidentify whether or not an external or internal defect is present.

[0007] The aim of the present invention is to provide ail apparatus andmethod which allows a fault to be detected using magnetic fluxmonitoring and furthermore, allow the accurate identification of whetherthe fault is positioned on the external surface of the pipeline orinternal surface of the pipeline and to do so without the need forvisual checking to be relied on.

[0008] In a first aspect of the invention there is provided apparatusfor the analysis of a pipeline condition, said apparatus mountable onthe external surface of the pipeline and including a means for inducinga magnetic flux into and at least partially through the wall of thepipeline adjacent the location of the apparatus and a means formonitoring the magnetic flux level and characterised in that there isprovided a sensing means at the external surface of the pipeline fordetecting a change in condition of the material of the pipeline.

[0009] In one embodiment, the apparatus is provided to be moved aroundand/or along a length of pipeline with changes in the magnetic flux andthe sensing means being monitored.

[0010] In one embodiment, the sensing means is a proximity sensor whichis used to determine a change in condition of or near to the externalsurface of the pipeline.

[0011] In one embodiment, the apparatus is particularly useful inrelation to a cast iron material pipeline, wherein the proximity sensorchanges in response to a change in the material structure and so allowsthe determination of a change in condition of the cast iron to beidentified and located so as to indicate, for example, the formation ofgraphite the external surface of the pipeline. The location of thegraphite would not be identifiable by a visual check of the cast ironpipe, in accordance with conventional methods.

[0012] In one embodiment, the apparatus includes a jacket which islocatable around the circumference of the pipeline and, at spacedlocations around the jacket, are located magnetic flux monitoring meansand proximity sensors.

[0013] In an alternative arrangement, particularly for pipes of largerdiameter, the apparatus is mounted on a track, with the track, in turn,being mounted along a section of the pipeline, said apparatus movingalong the track and the track and apparatus subsequently positioned atother locations around the circumference of the length of pipeline.

[0014] In one embodiment, the sensing means used for magnetic fluxdetection is a Hall effect sensor.

[0015] In a further aspect of the invention there is provided a methodfor the analysis and detection of changes in condition of a pipeline,said method comprising the steps of moving apparatus containing amagnetic flux inductor and detection means and a proximity sensor alongand/or around a portion of pipeline, monitoring the readings from themagnetic flux detector and the proximity sensor, identifying changes inthe magnetic flux and/or proximity sensor and characterised in that, achange in condition of both the magnetic flux and proximity sensorindicates the existence of a change in condition of or near to theexternal surface of the pipeline and a change in condition in themagnetic flux but not in the proximity sensor indicates a change incondition located on or near to the interior surface of the pipeline.

[0016] As the proximity sensor is used to monitor the change incondition of the external pipeline so changes in the material. Structureon or near the external surface can be differentiated from changes incondition on the internal surface of the pipeline and hence an accurateindication of the location of the change in condition of the pipelinematerial is provided. Furthermore, the extent of change in the proximitysensor and also extent of change of magnetic flux can be used todetermine the size and depth of the change in condition.

[0017] In one embodiment, the pipeline is made from cast iron and theproximity sensor indicates the existence of areas of graphite ratherthan cast iron material on or near the external surface of the pipelinewhich would not otherwise be detectable.

[0018] In one embodiment, the method includes the steps of removing asection of pipeline as a sample, performing the method on the same asindicated herein and then using the results of the condition of thepipeline sample to represent the condition of a length of the pipelinefrom which the sample was removed. In one embodiment, a one metre longsample of pipeline is used to reach a conclusion as to the condition of1,000 metres of pipeline. This has been adopted by many of the U.K WaterCompanies.

[0019] Over time, the method includes the step of building a history offaults and defects which are represented by particular detected magneticflux changes and/or proximity sensor changes and, in the subsequentanalysis of new samples of pipeline, reference is made to the historicdata to teach a conclusion as to the type and effect of the change incondition represented by detected readings.

[0020] A specific embodiment of the invention is now described withreference to the accompanying drawings, wherein:

[0021]FIG. 1 illustrates the conventional provision of magnetic fluxleakage along a pipeline;

[0022]FIG. 2 illustrates one embodiment of the invention in schematicmanner;

[0023] FIGS. 3A-E illustrate in mote detail, the schematic apparatusshown in FIG. 2; and

[0024] FIGS. 4A-H illustrate a further embodiment of the invention.

[0025] Referring firstly to FIG. 1, which is a schematic representationof the invention, there is shown the manner in which magnetic flux canbe generated in a pipeline 2 along which a liquid is moving as indicatedby arrows 4. In this case, on the interior wall of the pipeline there isa protrusion 6 which may be caused by, for example, corrosion. Themagnetic flux is induced by the conductor apparatus 8 and 10 whichcauses generation and movement of the magnetic flux as indicated by thearrows 12 and through the pipeline as indicated by the lines 14. Whenthe interior and exterior surfaces of the pipeline are smooth, andgenerally fault free the lines 14 will be generally parallel but theprovision of the protrusion 6, causes leakage of magnetic flux throughthe pipeline walls as indicated by the lines 14′. The change in magneticflux is monitored by the monitoring means 16.

[0026]FIGS. 2 and 3 illustrate one embodiment of the invention whichincorporates this feature of FIG. 1 and which also incorporatesadditional features which render the same inventive.

[0027] The example of the apparatus now described has been designed toinspect pipe work in the pipeline size range 3″ to 6″ diameterconstructed from any of the materials of cast iron, ductile iron, spuniron and steel.

[0028] In this version of the inspection tool, a jacket 19 is providedto fit around the pipeline and the magnetic flux flow circuit isdesigned to allow the electromagnets 20, 22 at each end of the apparatusdetector array to induce magnetic flux into the pipe section around thefull circumference of the pipe. Similarly, the flux leakage detectionelement 31 of the system is arranged to sense leakage at a number ofselected predetermined radial positions at points around the pipecircumference.

[0029] The elements of the detector array, jacket, magnetic fluxinduction and magnetic flux leakage, have been designed to allow thejacket 19 to split in half to two hinged parts 26, 28 to facilitateassembly onto and removal from the pipe.

[0030] The apparatus is fitted with wheels 30 and a suspension systemthat serve to facilitate movement of the apparatus along the pipesection 29 being inspected, and to maintain the required air gap betweenthe pipeline wall and the detector array. This system allows adjustmentsto be made in order to accommodate variations in pipe geometry.

[0031] A sensor ring 31, including the monitoring means in the form ofHall effect sensors 32, are incorporated to detect magnetic flux leakageand located in each or at selected intervals, proximity sensors 33 arealso fitted to enable the distinction and location of internal andexternal defects of the pipeline to be determined as the apparatus movesalong the same.

[0032] The proximity sensor is sensitive to the presence of the pipematerial beneath it. When passing along a pipe showing no orinsignificant corrosion a constant output signal in terms of volts wouldbe expected to be received from the proximity sensors. However, if achange in condition is detected on or near the external surface of thepipeline the proximity sensor reading will change.

[0033] A means (not shown) of recording distance moved by the detectorarray along the pipe section is also provided.

[0034] Another form of the apparatus, required for larger diameterpipes, is shown in FIGS. 4A-H although the magnetic fluxgenerator/leakage detection system, detector array is similar for bothdetection systems. However, in this embodiment, the apparatus is mountedon a track 40 which facilitates movement along the pipe section 42 underinspection with FIGS. 4C-4H illustrating the apparatus in use onpipelines with different diameters.

[0035] The track 40 is strapped to the pipe 42 to allow movement of thedetector array along the pipe section to be inspected.

[0036] The detector array is moved by pulling it by hand, along thetrack, thus scanning the pipe section below it.

[0037] The track is then moved in stages circumferentially around thepipe, by reducing the clamping action of the strap, to allow anotheradjacent pipe length to be inspected. This process continues until theentire pipe circumference has been inspected, the clamping straps arethen released and the whole assembly can be removed from the pipe.

[0038] The magnetic flux generator consists of two electromagnets 44, 46fixed to a connecting bar 48, which separates them and provides a returnmagnetic flux path between them. When this assembly is placed on thetrack above the pipe being inspected the pipe structure provides thefinal element in the magnetic flux flow path.

[0039] The magnetic flux leakage monitor 50 of the detector array 51 islocated between the electromagnets and consists of Hall effect sensorsfixed into a support frame, which not only accurately position thesensors above the pipe section but also places the sensors in apredetermined radial position. The proximity sensors are also locatedwithin the detector array.

[0040] The detector array 51 is fitted with a means of recording itsposition relative to the support track and hence in relation to the pipesection being scanned.

[0041] The support track can be fitted with handles on each side tofacilitate handling and transport to and from the inspection site.

[0042] The apparatus and method, when used with a pipe which has areasof corrosion present, can. identify a fault and where, in relation tothe pipeline, the fault is located. Considering a cast iron pipeline asan example, this material is characterised in that when corroding, theiron goes into solution leaving behind graphite flakes. Over a period oftime the cast iron structure becomes a composite of the original castiron and a graphite matrix. The graphite flakes not only retain theshape of the original pipe section but also camouflage the roughenedpipe subsurface and the true extent of the corrosion is not evident andthe original strength of the pipe section is considerably degraded. Thiscorrosion behaviour is also typical of cast or spun iron, ductile ironbut not of steel.

[0043] By using the apparatus and method of the invention, the proximitysensor can detect the interface between the graphite layer and theoriginal pipe material and register the change by change in voltage asthe detector array passes over the corroded area if that area is at ornear the external surface of the pipeline. However, the proximity sensordoes not react in this way when moving over an area of the pipe withcorrosion at or near the internal wall of the pipeline as the proximitysensor is set so as not to detect through the depth of the pipe wall. Inthis way the detector array can detect and distinguish between externaland internal corrosion, as firstly the magnetic flux detection detectscorrosion and the proximity sensor reacts if the corrosion is at or nearthe external surface of the pipeline.

[0044] In use the detector array is first assembled onto the pipesection, and then pulled over the section to be inspected and a means ofdetermining the relative position of the detector array on the pipesection is provided.

[0045] With both embodiments of apparatus the method of use is such thatthe severity and position of the effects and the remaining pipe wallthickness can be indicated by changes in flux leakage detected by theHall effect sensors which in turn are transmitted as a change in voltageto the data processing system and associated software.

[0046] In addition to this, the proximity sensors provide an indicationof whether the defects ate external or internal.

[0047] Software can be used which allows the interpretation of the Halleffect, proximity and detector array positional data in terms of defectsize, pipe wall thickness and geometrical orientation of the defects, toallow a report to be provided and, if necessary, a prediction of thelife expectancy of the pipework to be provided to allow improvedmaintenance planning.

1. Apparatus for the analysis of a pipeline condition, said apparatusmountable on the external surface of the pipeline and including a meansfor inducing a magnetic flux into and at least partially through thewall of the pipeline adjacent the location of the apparatus and a meansfor monitoring the magnetic flux level and characterised in that thereis provided a sensing means, at the external surface of the pipeline,for detecting a change in condition of the material of the pipeline. 2.Apparatus according to claim 1 characterised in that the apparatus ismovable around and/or along a length of pipeline with changes in themagnetic flux detected and the sensing means condition being monitoredat the different locations on said pipeline.
 3. Apparatus according toclaim 1 characterised in that the sensing means is a proximity sensorwhich is used to determine a change in pipeline material condition. 4.Apparatus according to claim 1 characterised in that the apparatus ispositioned on a cast iron pipeline with the proximity sensor changing inresponse to a change in the pipeline material to graphite at or near theexternal surface of the pipeline.
 5. Apparatus according to claim 4characterised in that the sensor indicates a change in condition of thecast iron to graphite in term of a variation in a monitored voltagereading.
 6. Apparatus according to claim 1 characterised in that theapparatus includes a jacket which is locatable around the circumferenceof the pipeline and, at spaced locations around the jacket, are providedmagnetic flux monitoring means and proximity sensors.
 7. Apparatusaccording to claim 1 characterised in that the apparatus is mounted on atrack, with the track, in turn, being mounted along a section of thepipeline, said apparatus movable along the track.
 8. Apparatus accordingto claim 7 characterised in that the track and apparatus arepositionable at selected locations around the circumference of thepipeline.
 9. Apparatus according to claim 1 characterised in that thesensing means used for magnetic flux detection is a Hall effect sensor.10. A method for the analysis and detection of changes in condition of apipeline, said method comprising the steps of moving apparatuscontaining a magnetic flux inductor and detection means and a proximitysensor along and/or around a portion of pipeline, monitoring thereadings from the magnetic flux detector and the proximity sensor,identifying changes in the magnetic flux and/or proximity sensor andcharacterised in that, a change in condition of both the magnetic fluxand proximity sensor indicates the existence of a change in condition ofor near to the external surface of the pipeline and a change incondition in the magnetic flux but not in the proximity sensor indicatesa change in condition located on or near to the interior surface of thepipeline.
 11. A method according to claim 10 characterised in that theproximity sensor is only used to monitor the change in condition of theexternal pipeline so the same can be differentiated from changes incondition on the internal surface of the pipeline.
 12. A methodaccording to claim 11 characterised in that an accurate indication ofthe location of the change in condition with respect to location on thepipeline and within the pipeline wall is provided.
 13. A methodaccording to claim 11 characterised in that the extent of change in theproximity sensor and also extent of change of magnetic flux are used todetermine the size and depth of the change in condition.
 14. A methodaccording to claim 10 characterised in that the method includes thesteps of removing a section of pipeline to form a sample, performing themethod as and using the results of the condition of the pipeline sampleto represent the condition of a length of the pipeline from which thesample was removed.
 15. A method according to claim 14 characterised inthat a one metre long sample of pipeline is used to represent thecondition of 1,000 metres of pipeline.
 16. A method according to claim10 characterised in that the method includes step of compiling a historyof faults and defects which are represented by particular magnetic fluxchanges and/or proximity sensor changes and, in the subsequent analysisof new samples of pipeline, reference is made to the historic data toreach a conclusion as to the type and effect of the change in conditiondetected.